1. Technical Field
The present invention relates to a separator for a battery comprising a gel polymer layer having a three-dimensional open porous structure, a method for preparing the same, and an electrochemical device comprising the same separator.
2. Background Art
Recently, there has been increasing interest in energy storage technology. Batteries have been widely used as energy sources in portable phones, camcorders, notebook computers, PCs and electric cars, resulting in intensive research and development. In this regard, electrochemical devices are subjects of great interest. Particularly, development of rechargeable secondary batteries has been the focus of attention.
Secondary batteries are chemical batteries capable of repeating charge/discharge cycles via reversible conversion between chemical energy and electric energy, and may be classified into Ni-MH secondary batteries and lithium secondary batteries.
A separator serves to prevent an internal short circuit caused by direct contact between a cathode and an anode of a lithium secondary battery and to allow ion penetration. A currently used separator is generally based on polyethylene (also referred to as ‘PE’ hereinafter) or polypropylene (also referred to as ‘PP’ hereinafter).
Meanwhile, conventional lithium polymer batteries use a separator on which a dense gel polymer layer is coated. Such a dense gel polymer layer is formed by dissolving a polymer into a solvent to form a coating solution and dipping a polyolefin-based separator into the coating solution.
U.S. Pat. No. 5,460,904 to A. S. Gozdz discloses a hybrid type polyvinylidene fluoride (also referred to as ‘PVdF’ hereinafter)-based polymer electrolyte. The hybrid type PVdF-based polymer electrolyte is obtained by imparting submicron-sized nanopores to a polymer matrix by using a plasticizer and injecting an organic electrolyte into the pores. However, in this case, an additional step of extracting the plasticizer contained in the polymer matrix is required, and thus the overall process is undesirably complicated. Additionally, if the plasticizer is not completely extracted from the polymer matrix, the remaining plasticizer may cause degradation of the quality of a battery. Moreover, a PVdF-based electrolyte shows poor adhesion to an electrode, although it has a relatively high mechanical strength.